Cold roller leveling treatment of cube oriented silicon steel to remove coil set

ABSTRACT

The present invention is a final treatment of cube oriented silicon steel, subsequent to the high temperature box anneal, to remove the coil set resulting from the box annealing. The final treatment includes a first step of roller leveling at ambient temperatures followed by an anneal at elevated temperatures between 700*C and 1300*C.

United States Patent [191 Foster Nov. 19, 1974 [54] COLD ROLLER LEVELING TREATMENT OF CUBE ORIENTED SILICON STEEL TO REMOVE COIL SET [75] lnventor: Karl Foster, Pittsburgh, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Oct. 26, 1973 21 App]. N0.: 410,133

[52] US. Cl 148/111, 148/112, 148/113 [51] Int. Cl. H01f 1/04 [58] Field of Search 148/111, 112, 113, 110,

148/31.55; 72/160, 161, 701, 702, DIG. 16

[56] References Cited UNITED STATES PATENTS 1,887,339 11/1932 Stroble 148/111 Scharschu 148/110 Ford et al. 148/112 Primary ExaminerWalter R. Satterfield Attorney, Agent, or FirmR. T. Randig [5 7] ABSTRACT 6 Claims, N0 Drawings TREATMENT OF CUBE ORIENTED SILICON STEEL TO REMOVE COIL SET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the treatment of silicon steel for electrical applications, and more particularly to a final treatment of the silicon steel, after the desired orientation has been achieved, to remove the coil set while maintaining optimum electrical properties. The method of the present application has particular application in the final treatment of the socalled cube oriented silicon steel. This is the so-called cube on face orientation and is indicated by the miller indicies (100) [001]. For the purpose of the present invention the term cube oriented will be used specifically to refer to this type of grain orientation. This is a different orientation from the so-called cube on edge orientation which is indicated by the miller indicies (1 I) [001] and is not to be confused therewith.

2. Description of the Prior Art In the production of the so-called cube oriented silicon steel, an ingot of steel of the proper chemistry is first formed and then, through successive rolling and coiling and heat treatment operations, the steel is processed until it is in coiled form of the desired thickness, with a final high temperature box anneal being given to the coiled strip of steel to complete the heat treating process and provide the desired cube oriented structure. As a result of this final high temperature box anneal and'subsequent cooling, the coil will take on what is known as coil set. This is a condition characterized by the fact that the coil will remain in the curved or convoluted condition and, in fact, must be plastically deformed to be returned to a flat or flattened condition which condition is the one which is normally required of this type of steel for its use in transformers and various other electrical devices. Hence the conventional prior art procedure following the high temperature box anneal has been to provide a continuous strip anneal at temperatures between 750C and 900 while simultaneously roller leveling with longitudinal tension applied to the steel to remove the coil set. While this method is effective to remove the coil set and provide a resultant product which inherently tends toward the flat condition, nevertheless the simultaneous annealing with roller leveling at the elevated temperatures has produced a certain degradation in electrical properties, particularly an increase in the core loss property of the material over what it is-in the box annealed condition prior to the treatment.

SUMMARY OF THE PRESENT INVENTION According to the present invention, a process of removing the coil set from a coil of cube oriented silicon steel which has been box annealed toform the desired orientation is provided in which the material is cold roller leveled at ambient temperature without longitudinal tension and thereafter annealed at a temperature between about 700C and l300C.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is specifically related to what is essentially a final treatment of cube oriented silicon steel following a final high temperature box anneal, the

final treatment being to remove the coil set, and when treated according to the present invention this final treatment will not materially degrade the electrical properties and particularly the core loss, the core loss being maintained essentially at the minimum developed by the final box annealing heat treatment.

As indicated above the conventional prior art final treatment after the box anneal has been to continuous anneal at high temperatures and concomitantly roller level at these high temperatures, i.e., 750C to 900C applying longitudinal tension to remove the coil set. This has resulted in an average core loss in cube oriented steel of about 1.03 watts/lb at 15 KG/Hz. However, it is known that inherently thes'e steels can attain a watt loss under these same test conditions of 0.83 to 0.85 watts per pound and thus the final treatment is, in fact, degrading. the electrical properties of the steel and producing a poorer quality of steel than has been or can be produced by the final high temperature anneal.

According to the present invention, the final treatment after the high temperature box anneal and cool is a two step treatment of first cold roller leveling without applying longitudinal tension for flattening the steel and then annealing the steel either as batch or continuously between about 700C and l300C, this final anneal being done in the absence of tension; i.e., only sufficient amount of tension is supplied to pull the material through the annealing furnace when the annealing is done as a continuous anneal as opposed to a batch anneal which, of course, requires no tension at all. While the broad temperature range of 700C to l300C may be utilized for the final annealing temperature, it is preferable that the temperature be between about 750C and 900C, basically for economic reasons in that in this range the heat treatment is completed in three to five minutes and any higher temperature does not materially speed up the process while with a lower temperature maintained between 700 and 750C requires a somewhat longer time to finish the final step.

Even more preferable the final anneal would be about 825C which will give an optimum time-temperature relationship, it being understood that this isfor ecothan about 700C do not produce the desired effect and those over l,300C are totally impractical based on the operating characteristics of commercially available equipment.

Also, in some cases it is desired to have a final glass coating on the material which is to be utilized for laminations. According to the present invention the glass frit which ultimately is fired to form the glass coating can be applied after the cold roller leveling and prior to the final annealing treatment so that the final annealing treatment can also function to fire the glass to form the desired coating. v

As indicated above the final annealing may take place either as a continuous annealing operation wherein the coil is pulled through the furnace, or alternatively the material after the cold roller leveling may be cut to the desired size and batch annealed,in either case the final anneal between 700 and l,300C serving to finish the treatment of the cube oriented silicon steel.

Test results have indicated that by utilizing the two ler leveling without longitudinal tension and thereafter annealing between 700 and 1,300C, the watt loss of the resulting product can be essentially minimized, there being no substantial degradation between the properties developed in the final high temperature box anneal. The table below shows test results comparing a specimen as batch annealed without any roller leveling, a specimen which was cold roller leveled following the box anneal, but which was not annealed subsequent to the cold roller leveling, a specimen that was cold roller leveled and then strip annealed at 850C, and a specimen which was cold rolled leveled and then batch annealed at 775C.

tension batch annealed 775C As can be seen from the table, the batch annealed specimen having no leveling, developed a watt loss of about 0.85 w/lb at 151(G and 1.30 w/lb at 17KG. This represents essentially the finally developed properties unaltered by any induced mechanical stresses and represents the minimum that should desirably be maintained after the final treatment of the material. Still referring to the table, it can be seen that when only a cold roller leveling treatment is given the watt loss jumps to about 1.02 w/lb at KG and 1.50 at 171(G. However, when this cold roller leveling treatment is followed by either a strip anneal or a box anneal, the watt loss is reduced to the approximate value which was developed by the box annealing. This indicates .that the final treatment according to this invention does not materially degrade or reduce the electrical properties represented by a watts loss developed by the silicon steel in the cube oriented configuration. As indicated above. according to the prior art treatment wherein the final anneal and the roller leveling are done concomitantly the average core loss has been about 1.03 w/lb at 15 KG/ Hz. Thus the present two step process represents a significant increase over the prior art process.

What is claimed is:

1. In the process of producing cube oriented silicon steel, wherein the steel has been high temperature box annealed and cooled in coiled form to provide the desired grain orientation which results in coil set, the method of removing the coil set comprising the steps of,

a. cold roller leveling the coiled material at ambient temperature without longitudinal tension and thereafter b. annealing the leveled material at a temperature between 700C and 1,300c.

2. The process as defined in claim 1, wherein the annealing temperature is between 750C and 900C.

3. The process as defined in claim I, wherein the coiled material is continuously strip annealed.

4. The process as defined in claim 1, wherein the material is cut to length subsequent to cold roller leveling, and the individual cut lengths are batch annealed.

5. The process as defined in claim 1, wherein a glass coating is applied to the strip subsequent to the cold roller leveling and prior to the annealing, said annealing being effective to fire the glass.

6. The process as defined in claim 1, wherein the annealing temperature is about 825C. 

1. IN THE PROCESS OF PRODUCING CUBE ORIENTED SILICON STEEL, WHEREIN THE STEEL HAS BEEN HIGH TEMPERATURE BOX ANNEALED AND COOLED IN COILED FORM TO PROVIDE THE DESIRED GRAIN ORIENTATION WHICH RESULTS IN COIL SET, THE METHOD OF REMOVING THE COIL SET COMPRISING THE STEPS OF, A. COLD ROLLER LEVELING THE COILED MATERIAL AT AMBIENT TEMPERATURE WITHOUR LONGITUDINAL TENSION AND THEREAFTER B. ANNEALING THE LEVELED MATERIAL AT A TEMPERATURE BETWEEN 700*C AND 1,300*C.
 2. The process as defined in claim 1, wherein the annealing temperature is between 750*C and 900*C.
 3. The process as defined in claim 1, wherein the coiled material is continuously strip annealed.
 4. The process as defined in claim 1, wherein the material is cut to length subsequent to cold roller leveling, and the individual cut lengths are batch annealed.
 5. The process as defined in claim 1, wherein a glass coating is applied to the strip subsequent to the cold roller leveling and prior to the annealing, said annealing being effective to fire the glass.
 6. The process as defined in claim 1, wherein the annealing temperature is about 825*C. 